Heretofore, curable compositions, which are cured by active energy rays such as ultraviolet rays and electron rays or by common heat, have been employed in practice for various applications of such as paint for plastic, paper, woodwork and inorganic materials; adhesives, printing ink, printed circuit boards and electrical insulation compounds. Over the years, desired have been further improvements in weather resistance and adhesion, with respect to printing ink, paints and adhesives, among other compounds. Further, known is ultraviolet ray curable ink-jet ink which is cured by ultraviolet rays as ink-jet ink employing these techniques. An ink-jet recording method employing the ultraviolet curable ink has become popular with respect to relatively low odor, rapid drying and capability of recording on a recording medium without ink absorption, and disclosed are ultraviolet curable ink-jet inks (please refer, for example, to patent documents 1 and 2). In this application, ink-jet ink is required to have a low viscosity and to form a stronger and more flexible layer. Providing plasticity by addition of a plasticizer in ink-jet inks is disclosed (please refer, for example, to patent document 3). However, this refers only to fusing type ink and there is no description in regard to ultraviolet curable ink-jet ink.
However, in utilizing such inks, there is a problem of the curing sensitivity tending to vary depending on the type of recording materials, and working environment.
Since ink utilizing a radical polymerization compound receives an oxygen inhibition effect, curing inhibition tends to result when an ink droplet volume is small. Further, ink utilizing a cationic polymerization compound (for example, refer to patent documents 4-7) exhibits no oxygen inhibition effect; however, it shows a problem of being easily affected by water content (humidity) at a molecular level.
Patent Document 1: Unexamined Japanese Patent Application Publication No. 6-200204 (hereinafter, referred to as JP-A)
Patent Document 2: Japanese Translation of PCT International Application Publication No. 2000-504778.
Patent Document 3: JP-A No. 8-3493
Patent Document 4: JP-A No. 2001-220526 (scope of claims, and examples)
Patent Document 5: JP-A No. 2002-188025 (scope of claims, and examples)
Patent Document 6: JP-A No. 2002-317139 (scope of claims, and examples)
Patent Document 7: JP-A No. 2003-55449 (scope of claims, and examples)